Does this sentence portray fronting or inversion?
Only later did it become evident that they were not satisfied with the offer.
Does this sentence portray fronting or inversion?
Only later did it become evident that they were not satisfied with the offer.
Only later did it become evident that they were not satisfied with the offer.
It has subject-auxiliary inversion as a result of fronting.
This occurs in declarative clauses only when certain types of element are put in front position. Negatives are one very obvious type of element that trigger subject-auxiliary inversion when fronted:
Never had I seen such chaos.
At no stage were they in danger.
"Only" is not negative, but it is semantically close to a negative, in that "Only John liked it", for example, entails "No one other than John liked it". The inversion is also found with some items that are not similar to negatives:
John enjoyed it and so did Robert.
Sample: Only later did it become evident that they were not satisfied with the offer.
It can be the inversion of:
So it's inversion with emphatic do-support with did. Do-support is required in inversions. You cannot do this: Only later it became evident...that is agrammatical in English.
If you remove the emphatic do (do-support), it would read as below and be a re-writing:
And "only later" in that construction can be considered fronting in the sample as that adverbial phrase usually goes after the verb.